Gastrointestinal tract intestinal peristalsis

The innervation of the gastrointestinal tract is complex. The myenteric and submucosal plexuses contain many interneurons. These possess a number of neurotransmitters and neuromodulators, including several peptides, such as enkephalins, substance P, and vasoactive intestinal peptide. Reflex activity within the plexuses regulates peristalsis and secretion locally. The effects of sympathetic and parasympathetic nerve stimulation are superimposed on this local neural regulation. 

The gastrointestinal tract is the only system outside the central nervous system (CNS) with significant concentrations of opioid receptors. This reflects their common embryonic origins. Opioids increase intestinal tone and decrease propulsive peristalsis, resulting in delayed gastric emptying and constipation or ileus. Opioids increase common bile duct pressure and decrease bile production and flow, primarily because of spasm of the sphincter of Oddi. The tone of the bile duct itself is also increased. 

Smooth muscle is relaxed. In the gastrointestinal tract there is reduction of tone and peristalsis. Muscle spasm of the intestinal tract induced by morphine is reduced, but such spasm in the biliary tract is not significantly affected. Atropine relaxes bronchial muscle, an effect that is useful in some asthmatics. Micturition is slowed and urinary retention may be induced especially when there is pre-existing prostatic enlargement. 

Gastrointestinal Increases the tone and motility of the smooth muscles of the stomach and intestine. Peristalsis is increased and the sphincter muscles are relaxed. Relaxes smooth muscle tone of GI tract, decreasing GI motility and peristalsis. Decreases gastric and intestinal secretions. 

Caffeine relaxes smooth muscle of the biliary and gastrointestinal tracts and has a weak effect on peristalsis. However, high doses can produce biphasic responses, with an initial contraction followed by relaxation. Caffeine seems to have no effect on the lower oesophageal sphincter. The increase in both gastric and pepsin secretions is linearly related to the plasma levels obtained after the administration of a dose of 4-8mgkg . In the small intestine, caffeine modifies the fluid exchange from a net absorption to a net excretion of water and sodium. 

GASTROINTESTINAL AND URINARY TRACTS Although stimulation of vagal input to the gastrointestinal (GI) tract increases tone, amplitude of contraction, and secretory activity of the stomach and intestine, such responses are inconsistently seen with administered ACh. Poor perfusion of visceral organs and rapid hydrolysis by plasma butyrylcholinesterase limit access of systemically administered ACh to visceral muscarinic receptors. Parasympathetic sacral innervation causes detrusor muscle contraction, increased voiding pressure, and ureter peristalsis, but for similar reasons these responses are not evident with administered ACh. 

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